Diesel fuel



Patented Sept. 10, 1940 UNITED STATES DIESEL FUEL Eugene Lieber, Linden, N. J., and Pharis Miller, Des Moines, Iowa, assignors to Standard Oil Development Company, a corporation of Delaware , No Drawing. Application July 14, 1938,

Serial No. 219,158

3 Claims. (01. 44-9) This invention relates to improved Diesel fuels and methods for preparing the same. More particularly, this invention relates to the incorporation of a novel type of ignition-promoting agent into a hydrocarbon Diesel fuel stock, such as a gas oil fraction of petroleum originj'this novel type of agentbeing a compound containing an active linkage in an oxy-nitrogen sulfur group i attached to carbon. such as a nitrosyl mercaptan, and possessing suitable solubility in the oil, resistance to hydrolysis, and properties for conferring on the fuel undergoing combustion in a compression-ignition engine excellent ignition qualities. v m In consideration of increasing the power, fuel economy, and the reduction of vibration in the operation of compression-ignition engines when the hydrocarbon fuel contains insufficient amounts of the compounds recognizable as serving these ends, the additions of various non-hydrocarbon compounds, often spoken of as dopes, such as certain nitroso compounds and alkyl polysulfides have been proposed. Some of these dopes have been represented as being explosive primers for initiating the ignition at low temperatures. a In many instances the addition agents or dopes proposed by the prior art have been diflicult to use. Some are too volatile and therefore reduce the flash poin of the doped fuel to below a safe temperature. ome must be added in large amounts to be effective and in such amounts may produce undesirable amounts of corrosive combustion products Some are unstable when exposed to moisture, and some are too explosive.

Ignition qualities of a compression-ignition fuel are promoted not only by an easy starting of the ignition but also by other factors comprising combustion with regulated rapidity to avoidvtoo abrupt accumulation of pressure which causes detonation.

A prime consideration in the use of addition agents or dopes for Diesel fuels, aside from their beneficial effects on the ignition qualities of the fuel and detrimental efi'ects, is the cost. It can be readily seen that substances which can be manufactured by simple reactions from by-products available in large quantities at petroleum refineries have decided advantages in their favor for low cost production. i

, In the interest of improving compression-ignition fuels from all aspects, many organic compounds containing sulfur, nitrogen and oxygen 4 have been tested and in accordance with this invention' it has been found that organic compounds containing an oxy-nitrogen sulfur group attached to-carbon, are efliciently and economically useful in this object. The eifectiveness of these compounds is surprisingly high compared with other nitrogen and sulfur containing compounds and accordingly is ascribed to the activ ity of their characteristic linkage, which may be graphically depicted as having some of the following structures and compositions:

These structures are capable of considerable modification and may be attached to a wide variety of organo radicals, but it is mainly essential that the oxy-nitrogen group be attached to carbon in an organic radical through a sulfur atom. The following types of compounds containing active oxy-nitrogen sulfur groups may be used in accordance with the present invention:

Nitrosyl mercaptans or thionitrites having th general structural formulae: RSNO or where R is an organo group such as an aliphatic,

or cyclic hydrocarbon radical, which may contain branched groups, e. g., ethyl nitrosyl mercaptan CHaSNO, isopropyl thionitrite (CH3) zCSNO, and triphenylmethyl thionitrite, (C6113) 3CSNO.

Sulphonium nitrates having the general structural formula:

where R stands for organo groups linked by three valence bonds to the sulfur, e. g., triethyl sulfonium nitrate (Cal-I5) 3SNO3, and methyl diethyl sulfonium nitrate ((JzHshzCfIsSNOa.

Sulfonyl hydroxyl amines are represented by RSOZNHOH in which R is an organo group, e. g., benzene sulfonyl hydroxyl amine. Organic sulfur compounds, such as mercaptans and their derivatives, recovered in abundance in desulphurizing petroleum oils are by-products which have fuel value but which have been in general worthless for use in fuels on account of their offensive odor and the acidic nature of their combustion products. The mercaptans are represented by the general formula RSH, R being a hydrocarbon radical, and their resemblance to alcohols makes them known as thio-alcohols. Alkyl thionitrites, which form a preferred class of ignition-promoting agents in the present invention,

may be regarded as esters of nitrous acid and thioalcohols.

, isomers.

It has been found possible to change mercaptans easily by reaction with nitrosyl chloride, NOCI, or; its equivalents, such as alkyl nitrites or nitrousyacid, into compounds having a general formula RSNO, in which R is a hydrocarbon radical, for example, an alkyl or an aryl. radical. A specific example is the reaction of butyl mer-. cap'tan, C4H9SH, with nitrosyl chloride at about "5 C. to -10 C. to form butyl nitrosyl mercap tan. When the reaction is substantially completed as indicated by greenish color of thick layers, the product may be purified simplyby washing with a cold alkaline solution and cold water. I The general reaction may be'represented by RSH+NOC1- RSNO+HCL Although the mercaptan class of comounds recovered .as by-products in petroleum refineries includes numerous compounds having various hydrocarbon radicals attached to the 4H group, by specific procedures for extraction of the mercaptans, as for example by an alkaline wash, and fractionation of the steam distilled extract, the

'various types of mercaptans can be separately concentrated. Specific fractions of mercaptans having certain alkyl groups, normal or branched,

attached to the SH radical, e.g,, the butyl mercaptans, and closely related mercaptans can thus beconcentrated. Among the related mercaptans which maybe used are ethyl, propyl, amyl, -hexyl, hepty1, and octyl mercaptans including the iso, primary, secondary, and tertiary In general, suchunercaptans and re.- lated organic sulfur compounds, whether recovered in petroleum refining or prepared syntheti: cally, are considered suitable for preparing the promoters in accordance with the present invention in so far as they permit the linking of an oxy-nitrogen group to the sulfur atom, whether this be obtained by any ofthe well known methods, such, as substitution, addition, reaction with an oxy acid of nitrogen, etc. For example; double decomposition reactions of mercaptans and mercaptide with nitrites or nitric oxide in the following ways are contemplated:

where R and R. represent organic radicals and M represents a metal in a mercaptide. The latter type of reaction is particularly advantageous if an active metal is present in the'mercaptide, because both products may then be used together or singly as addition agents.

. The organic oxy-nitr'ogen sulfur compounds described may be added in concentrations ranging from a fraction of 1% up to the limit of solubility in the fuel, but preferably from .025 to 3% to a hydrocarbon oil of suitable range for use as fuel in compression-ignition engines of the Diesel type. A gas oil boiling from 400 F. to 700 F;, or 750 F. may be used. Under some circumstances, a more'narrowly cut fractionsuch as one distilling from about 400 to 600 F. or from tans, have been found to -'lead to the/production "of nitrosyl mercaptans' which are most e'ifective ignition-promoters in Diesel fuels'." I

The effectiveness'of tertiary butyl nitrosyl'merthat they p drm 59.

captan is demonstrated by the following tabulated results:

Cetane number colombla gas or In testing the efilcieney of these promoters the cetane number is recommended as a good standard of evaluation by the S. A. E. Volunteer Group for Compression-Ignition Fuel Research. This test is described in the S. A. E. Journal of June 1936, page 225, andconsists in a performance 'comparisonpof the fuel to betested with blends of cetane and alphamethyl-naphthalene. The percent cetane in the blend with the alphamethyl-naphthalene to give the same ignition quality test performance as the fuel in question is taken as the cetane number of. that fuel. Normal cetane serves as a standard of high ignition .quality in Diesel fuel rating analogously to. the

way iso-octane is used as a standard of high anti: knock in gasoline rating.' Normal cetane has a very short ignition lag in a compression-igni ion engine, whereas alphamethyl-naphthalene on be contrary has a long lag associated with poor lgnition quality, and for a blend of these two hydrocarbons the ignition quality in terms of lgnition lag is nearly inversely proportional to the concentration of the cetane. passes between the beginning'of the fuel injection into the combustion chamber of the test engine and the point at which ignition of the fuel sets in is called the ignition lag which may be expressed in degrees of crank angle or in time units.

The tabulated results on the effect of varying small percentages of the nitrosyl'mercaptan in 9. Diesel fuel evince the excellent effectiveness of these compounds in improving ignition quality of the Diesel fuel as expressed by cetane number. The cetane number increase is a measure of the reduction in time lag and detonation effected by the nitrosyl mercaptan in terms of the corresponding improvement made by such an increase in percent of normal cetane in a blend with.alphamethyl-naphthalene. a

The small quantities of organic sulfur oxy-nitrogen compounds added for a subst provement of the Diesel fuel do not increase the sulfur content of the treated fuel excessively. It is recognized that a high'content of sulfur may -be considered undesirable in the. operation of tial imv The time which moters of this invention have the creditable property of being resistant to hydrolysis by water,

1 the preparation of Diesel fuels giving satisfac-,

tory engine performance from crude oils, gas oils,

.andresidual. fuels having low pour points, low

A. P. I. gravities, and high heat values, procured frqml naphthene base, asphalt base, and mixed base crudes, since the addition in small quantities of the nitrosyl mercaptan ignition-promoters improves their ignitQg qualities to the extent factorily particularly v11 2,214,059 high speed Diesel engines. -The burning qualities of gas oils from parafiine crudes are also enhanced by the nitrosyl mercaptans. Ordinarily, the hydrocarbon fuel with which the promoter is blended for use in Diesel type engines has a boiling range above that of gasoline.

Small quantities of this promoter may be used for adapting various mixtures of. hydrocarbons for useas Diesel fuels, including recycle reflux from a cracking operation, oils from destructive distillations of pyro-bituminous and .asphaltic miaterials, non-parafiinic extracts, and mixtures of these with one another or with crude petro-,

leum fractions. .Other agents for enhancing various qualities without detracting substantially from the ignition qualities of the fuel, such as oiliness agent s, sludge dispersers, dyes, corrosion inhibitors, anti-oxidants, viscosity-improvers, and pour point depressants may be admixed with the fuel as desired in addition to the'nitro syl mercaptan. Also, other promoters may be admixed. l

It is not intended that this invention be limited to the specific examples which are given merely for the sake of illustration. It is intended to claim all the novelty inherent in the invention as broadly as the prior art permitsin the appended claims.

1. A fuel for compression-ignition engines. of

the Diesel type comprisingessentially a hydrocarbon fuel with which is blended a minor proportion of a tertiary alkyl nitrosyl mercaptan; 2. A fuel for compression-ignition engines of the Diesel type comprising essentially a hydrocarbon fuel with which is blended a minor proportion of tertiary butyl nitrosyl mercaptan. 3. A fuel for compression-ignition engines of the 'Diesel typecomprising essentially gas oil petroleum hydrocarbons and about 0.25 to 3% of tertiary butyl nitrosyl' mercaptan.

EUGENE IJEBER. PHARIS MILLER. 

